Enhanced oil recovery with high molecular weight polyvinylamine formed in-situ

Abstract

The recovery of oil or gas from underground porous formations bearing such hydrocarbons is enhanced by using an injection fluid containing a viscosifying amount of a poly(vinylamine) formed in-situ by hydrolysis of a high molecular weight poly(N-vinylamide). The hydrolysis conditions are strongly acidic or highly alkaline and include the elevated temperature of the formation. The poly(N-vinylamide), such as poly(N-vinylformamide), can be made by inverse emulsion polymerization and the high solids emulsion mixed directly with the acidic or basic solutions to form the injection fluid. The process is applicable to enhanced oil recovery using fluids for water-flooding, well completion or workover, and acidifying or fracturing.

We claim: 
     
       1. A process for enhancing the recovery of oil or gas from a porous underground formation bearing oil or gas which comprises injecting into said formation an aqueous fluid containing from about 0.1 to 2 weight percent of substantially unhydrolyzed poly(N-vinylamide) having an average molecular weight of at least 10 6 , which is homopolymer or copolymer of monomers having the formula: ##STR3## wherein R 1  and R 2  are each independently H or C 1  -C 4  alkyl; and subjecting said poly-(N-vinylamide) within said formation to strongly acidic or strongly basic hydrolyzing conditions, thereby converting said poly(N-vinylamide) in situ to a viscosifying amount of poly(vinylamine) within said aqueous fluid. 
     
     
       2. The process of claim 1 wherein said poly(N-vinylamide) has an average molecular weight in the range of 1.3 to 15×10 6 . 
     
     
       3. The process of claim 2 wherein said poly(n-vinylamide) has an average molecular weight in the range of 1.8 to 9×10 6 . 
     
     
       4. The process of claim 1 wherein less than 10 percent of the amide moieties in the poly(N-vinylamide) are hydrolyzed to amine groups prior to injecting said fluid into said formation. 
     
     
       5. The process of claim 1 wherein said poly(N-vinylamide) is a homopolymer of N-vinylformamide, N-vinylacetamide or an N-substituted alkyl derivative of either amide. 
     
     
       6. The process of claim 1 wherein said strongly acidic conditions include a pH of about 2 or less and said strongly basic conditions include a pH of about 12 or more. 
     
     
       7. The process of claim 1 wherein said poly(N-vinylamide) has been prepared by inverse emulsion polymerization and the emulsion product of said polymerization is added to an acidic or basic water solution to form said aqueous fluid for injection into said formation. 
     
     
       8. The process of claim 1 wherein said poly(N-vinylamide) is less than 50 percent hydrolyzed to vinylamine units before entering said formation. 
     
     
       9. A process for enhancing the recovery of oil or gas from a porous underground formation bearing oil or gas which comprises mixing together an acidic or alkaline aqueous solution and a water-in-oil emulsion of at least 10 6  average molecular weight poly(N-vinylamide) formed by polymerizing N-vinylamide in an inverse emulsion, thereby forming an injection fluid containing from about 0.1 to 2 weight percent of said poly(N-vinylamide); injecting said fluid into said formation; and subjecting said poly(N-vinylamide) within said formation to strongly acidic or strongly basic hydrolyzing conditions to convert said poly(N-vinylamide) to poly(vinylamine) in sufficient amount to produce a viscosifying effect. 
     
     
       10. The process of claim 9 wherein the concentration of acid or base in the injection fluid is from the stoichiometric amount required for complete hydrolysis of the polymer amide groups present up to about 30 weight percent of the aqueous solution. 
     
     
       11. The process of claim 10 wherein said poly(N-vinylamide) is poly(N-vinylformamide). 
     
     
       12. The process of claim 10 wherein said injection fluid is an alkaline flooding fluid. 
     
     
       13. The process of claim 10 wherein said injection fluid is an acidic flooding fluid. 
     
     
       14. The process of claim 10 wherein said injection fluid is a well completion fluid. 
     
     
       15. The process of claim 10 wherein said injection fluid is a well acidizing solution.